Embodiments of the disclosure relate to an amplifier for multiple non-continuous (i.e., bursted) signals. There are many systems (commercial cell phone, radar, wireless communications, wireless networks, etc.) where multiple signals on different carrier frequencies are simultaneously transmitted and therefore require a great amount of peak power handling capability when the voltage peaks of the individual signals coincide in time. What is needed is a system and method that reduces the likelihood of the waveform peaks coinciding in time while still maintaining waveform performance.
Many wireless systems (radars, communication systems, networks, etc.) have multiple unique signals being transmitted simultaneously through a single radio frequency (RF) front end and/or antenna aperture. The analog circuitry must be designed to handle the summed average power of the multiple signals as well as the summed peak power of the multiple signals. Many times, the concurrent voltage peaks of the simultaneous signals either drive high peak power handling requirements in the front end analog circuitry or cause non-linear undesired effects when they surpass the peak power linearity rating of the front end circuitry. These undesired peak power issues occur when strong voltage peaks in the simultaneous signals align in time and cause a large power spike in the analog front end.
Prior art transmission systems will now be described with reference to FIGS. 1-5. FIG. 1 illustrates a prior art transmission system 100. As shown in the figure, transmission system 100 includes: a plurality of signal generators, a sample of which are indicated as a signal generator 102, a signal generator 104, a signal generator 106; a pre-processor 108; a high power amplifier (HPA) 112 and a transmitter 114.
Signal generators 102, 104, and 108 are arranged to communicate with pre-processor 108 via a communication channel 116. Pre-processor 108 is additionally arranged to communicate with HPA 112 via a communication channel 118. HPA 112 is additionally arranged to communicate with transmitter 114 via a communication channel 120.
In operation, the plurality of signal generators may generate respective bursted, or non-continuous, signals. For example, signal generator 102 generates a non-continuous signal 117 for transmission, signal generator 104 generates a non-continuous signal 119 for transmission and signal generator 106 generates a non-continuous signal 121 for transmission. Non-continuous signals 117, 119 and 121 are provided to pre-processor 108.
Pre-processor 108 may process non-continuous signals 117, 119 and 121 in any known manner to address cross-channel interference that might be created in HPA 112, so as to output a pre-processed signal indicated by arrow 128.
HPA 112 will sum and amplify the pre-processed signals and output an amplified signal 130 to transmitter 114. Transmitter 114 will transmit an output signal 132 based on amplified signal 130.
Typically HPA 112 will be driven very close to saturation, wherein it is most efficient. Because HPA 112 is driven close to saturation it must be designed such that the maximum amplitude of the sum of all the pre-processed signals, at any single time, does not exceed its saturation point.
Cellular transmission towers, that are similar to prior art transmission system 100, are typically designed to handle thousands of simultaneous signals. Accordingly, there is a high likelihood that at any given moment, many if not all of the handled signals will individually have a maximum amplitude. Therefore an HPA in such a cellular communications tower would be designed to handle a large number of pre-processed signals, whose amplitudes at any time may be summed and still not push the HPA beyond its saturation point.
Although such an HPA might not be driven close to saturation, and thus not optimally efficient, all the time, it is likely to be driven close to saturation, and thus optimally efficient, most of the time.
Some transmission systems do not need to handle a large number of signal generators at a single time. For example, some military mobile communication platforms are designed to transmit a predetermined low number of signals. This will be described with reference to FIG. 2.
FIG. 2 illustrates another prior art transmission system 200. As shown in the figure, transmission system 200 includes a signal generator 202, a signal generator 204, a pre-processor 206, an HPA 208 and transmitter 114.
Signal generator 202 is arranged to communicate with pre-processor 206 via a communication channel 210. Signal generator 204 is arranged to communicate with pre-processor 206 via communication channel 210. Pre-processor 206 is additionally arranged to communicate with HPA 208 via a communication channel 212. HPA 208 is additionally arranged to communicate with transmitter 114 via a communication channel 214.
In operation, signal generator 202 generates a non-continuous signal 216 for transmission and signal generator 204 generates a non-continuous signal 218 for transmission. Non-continuous signals 216 and 218 are provided to pre-processor 206. Pre-processor 206 may process non-continuous signals 216 and 218 in any known manner to address cross-channel interference that might be created in HPA 208, so as to output pre-processed signals represented by arrow 220.
HPA 208 will sum and amplify pre-processed signals and output an amplified signal 222 to transmitter 114. Transmitter 114 will transmit an output signal 224 based on amplified signal 222.
Again, HPA 208 will be designed so as to be driven very close to saturation, wherein it is most efficient. Because HPA 208 is driven close to saturation it must be designed such that the sum of the maximum amplitude of each of the pre-processed signals at any single time does not exceed its saturation point.
As opposed to transmission system 100 discussed above, which may include a large number of signal generators, in transmission system 200, HPA 208 has been designed to optimally work near saturation so as to amplify a combination of two input signals, namely non-continuous signal 216 and non-continuous signal 218. In particular, HPA 208 will be designed such that its saturation point is near the sum of the maximum amplitude of the sum of each of the pre-processed signals corresponding to non-continuous signal 216 and non-continuous signal 218.
HPA 208 might not optimally operate when the sum of the maximum amplitude of each of the pre-processed signals at any single time is not near the saturation point, which will likely be much of the time as there are only two signals. However, this system is designed to support a fixed predetermined number of input signals.
If another signal generator is added to transmission system 200, then there may be instances when the combination of input signals surpasses the saturation point of HPA 208, thus drastically reducing the signal to noise ratio of amplified signal 222. This will be described in greater detail with reference to FIGS. 3-4.
FIG. 3 illustrates another prior art transmission system 300. As shown in the figure, transmission system 300 includes: a plurality of signal generators, a sample of which are indicated as signal generator 202, signal generator 204 and a signal generator 302; pre-processor 206, HPA 208 and transmitter 114.
Signal generator 202 is arranged to communicate with pre-processor 206 via a communication channel 304. Signal generator 204 is arranged to communicate with pre-processor 206 via communication channel 304. Signal generator 302 is arranged to communicate with pre-processor 206 via communication channel 303. Pre-processor 206 is additionally arranged to communicate with HPA 208 via communication channel 212. HPA 208 is additionally arranged to communicate with transmitter 114 via communication channel 214.
Transmission system 300 differs from transmission system 200 of FIG. 2 discussed above, in that transmission system 300 included additional signal generators, a sample of which is indicated as signal generator 302. In operation, the plurality of signal generators generate respective non-continuous signals, a sample of which are indicated as non-continuous signal 216 from signal generator 202, non-continuous signal 218 from signal generator 202 and non-continuous signal 306 from signal generator 302. The plurality of generated signals is provided to pre-processor 206.
Pre-processor 206 may process the plurality of signals in any known manner to address cross-channel interference that might be created in HPA 208, so as to output pre-processed signals represented by arrow 308.
HPA 208 will sum and amplify the pre-process signals and output an amplified signal 310 to transmitter 114. Transmitter 114 will transmit an output signal 312 based on amplified signal 310.
Again, in this example HPA 208 had been designed so as to be driven very close to saturation, wherein it is most efficient. Further, in this example, as discussed above with reference to FIG. 2, HPA 208 had been designed such that the sum of the maximum amplitude of each of the pre-processed signals, which only included non-continuous signal 216 and non-continuous signal 218, at any single time would not exceed its saturation point.
However, in this example, HPA 208 is amplifying the pre-processed signals, which includes non-continuous signal 216 and non-continuous signal 218, in addition to a plurality of other generated signals, such as signal 306. Accordingly, in transmission system 300, there is a possibility that the combination of input signals from the plurality of additional signal generators will result in instances of the sum of the maximum amplitudes of each of the pre-processed signals being greater than the input voltage of HPA 208 as driven at saturation. This will be described in greater detail with respect to FIGS. 4A-C.
FIG. 4A illustrates a graph 400 associated with a signal 410 of signal generators 202 and 204 of transmission system 300 of FIG. 3. FIG. 4B illustrates a graph 402 associated with a signal 416 of signal generator 302 of transmission system 300. FIG. 4C illustrates a graph 404 associated with a sum of signal 410 and signal 416.
Graph 400 has a y-axis 406 of voltage and an x-axis 408 of time. Graph 402 has a y-axis 412 of voltage and an x-axis 414 of time. Graph 404 has a y-axis 418 of voltage and an x-axis 420 of time.
It should be noted that signal 410 in graph 400 is provided for discussion purposes only, wherein the signals generated by signal generator 202 and signal generator 204 are not independently added together separately from the signals generated by the other signal generators. In particular the graphs of FIGS. 4A-C are provided to illustrate a problem when an additional signal generator is added to a transmission system that has an HPA that is designed for less than the number of signal generators being used, which is the situation described above with reference to transmission system 300 of FIG. 3.
As shown in graph 400, signal 410 has a maximum amplitude of approximately 1.0 milli-Volts (mV) at position 424, which corresponds to a time of 125 milliseconds (ms). As shown in graph 402, signal 416 has a maximum amplitude of approximately 1.0 mV at position 426, which corresponds to the time of 125 ms, which is indicated by dotted line 428. The superposition (sum) of signal 410 and signal 416 is illustrated as signal 422 in graph 404. Signal 416 has a maximum amplitude of approximately 2.0 mV at position 430, which corresponds to the time of 125 ms, which is along dotted line 428.
For purposes of discussion, let HPA 208 operate at saturation at a voltage of 1.5 mV. If such is the case, in FIG. 4C, at the time of 125 ms, identified by dotted line 428, the amplitude of signal 422 will surpass the saturation of HPA 208. Accordingly, at the time of 125 ms, amplified signal 310 that is output by HPA 208 will have an unacceptable amount of distortion, or in other words, an unacceptable signal to noise ratio.
To address this issue of distortion, when additional signal generators are added to transmission system 200, for example to create transmission system 300, a new HPA must be designed and provided. This will be described with additional reference to FIG. 5.
FIG. 5 illustrates another prior art transmission system 500.
As shown in the figure, transmission system 500 includes: the plurality of signal generators, a sample of which are indicated as signal generator 202, signal generator 204 and signal generator 302; pre-processor 206, an HPA 502 and transmitter 114.
Transmission system 500 is similar to transmission system 300 discussed above with reference to FIG. 3, but differs in that HPA 208 of transmission system 300 has been replaced with an HPA 502 in transmission system 500.
In operation, the plurality of signal generators generate respective non-continuous signals, a sample of which are indicated as non-continuous signal 216 from signal generator 202, non-continuous signal 218 from signal generator 202 and non-continuous signal 306 from signal generator 302. The plurality of generated signals is provided to pre-processor 206.
Pre-processor 206 may process the plurality of signals in any known manner to address cross-channel interference that might be created in HPA 502, so as to output the pre-processed signals represented by arrow 308. HPA 502 will sum and amplify the pre-processed signals and output an amplified signal 504 to transmitter 114. Transmitter 114 will transmit an output signal 506 based on amplified signal 504.
Again, in this example HPA 502 has been designed so as to be driven very close to saturation, wherein it is most efficient. Further, in this example, as compared to HPA 208 as discussed above with reference to FIG. 3, HPA 502 had been designed such that the sum of the maximum amplitudes of each of the pre-processed signals, at any time, would not exceed its saturation point.
In the prior art transmission systems discussed above, there are two separate options. Option one, a transmission system is created that can support a large number of signal generators, wherein the HPA is driven near saturation most of the time. Option two, an HPA is designed for a predetermined, smaller, number of signal generators, wherein the HPA is driven near saturation some of the time.
What is needed is a transmission system that may use an non-predetermined number of signal generators, wherein the HPA is driven near saturation some of the time. For example, a transmission system that may use an original number of signal generators, wherein the HPA is driven near saturation some of the time, and that may be modified to add additional signal generators, wherein the HPA will continue to be driven near saturation some of the time.